High frequency induction furnace or heating apparatus



Dec- 15, 1931- v. ENGELHARDT ET AL 1,837,031

HIGH FREQUENCY INDUCTION FURNACE 0R HEATING APPARATUS Filed July 20.1927 4 Sheets-Sheet 1 22:: 6 I :2: 5 7/9. I /1 n? War-0R INGELh/A R07"WEINb/OLD GROSS BY 14%; flaw/1m u ATTO RA/e f5 Dec. 15, 1931. v.ENGELHARDT ET AL 1,337,031

HIGH FREQUENCY INDUCTION FURNACE OR HEATING APPARATUS Filed July 20,1927 4 Sheets-Sheet 2 IMvEn Ton's V/cTo/e I'MGELIJAROT REM MOLD GflossBY fiK MMAM A TTo-RME-K D 15, 1931- v. ENGELHARDT ET AL 1,837,031

HIGH FREQUENCY INDUCTION FURNACE OH HEATING APPARATUS 4 Sheets-Sheet 3'Filed July 20, 1927 v. ENGELHARDT ET AL 1,337,031

Filed July 20. 1927 4 Sheets-Sheet 4 aim-iii.

Dec. 15, 1931.

HIGH FREQUENCY INDUCTION FURNACE on HEATING APPARATUS Jill Patented Dec.15, 1931 UNITED STATES PATENT OFFICE VIUIOR ENGELHABCDT, OIBEB-LIN-CHABLOTTENBURG, AND REINHOLD GROSS, F EOHENNEUENDOBF, NEARBERLIN, GERMANY, ASSIGNORS TO SIEMENS 6t HALSKE, AKTIENGESELISCHAFT, 0]BIEHENSSTAUE, NEAR BERLIN, GERMANY, A CORPORA- T1018 01' GEBIANY HIGHFBEQUEVCY INDUCTION FURNACE OR HEATING APPARATUS Application fled July20, 1927, Serial No. 207,169, and in Germany July 24, 1926.

This invention relates to a high frequency induction furnace or-heatingapparatus. In the hitherto known high frequency induct on furnaces orheating apparatus, the nducing 6 coil is arranged outside thematerial tobe melted or heated through. In such case therefore the material isstruck only by the electromagnetic lines of force flowing in theinterior of the coil field, whilst the portion of the magnetic fluxpassing outside the coil,

is wasted without being utilized for the generation of the melting orheating heat.

Another drawback of the high frequency coil arranged outside thematerial to be melt- 1 ed or heated, is that the lines of force passingoutside the coil, make impossible the use of metallic materials forenclosing or strengthening the furnace, as these lines of force wouldproduce an inadmissible heating 2 of metallic parts of the furnace.

The invention avoids these drawbacks by the fact that according to theinvention the heat produced by induction in the charge material, isgeneratedby a heating coil dipped .25 or inserted into the chargematerial situated in the furnace interior. All the electro-magnetic lnes of force produced by the high freqi enc'y coil in the material to bemelted or heated, can be therefore-utilized for the heating or meltingprocess. Owing to the new arrangement, more particularly the heatingeffect is considerably increased and consequently the total efliciencyof the furnace or' of the heating apparatus considerably improved.

- Several constructions according to the invention are illustrated byway of example in the accompanying drawings.

Figures 1 and 2 show diagrammatically a 4 construction of the newinduction furnace in vertical and horizontal section. Figures 3 and .4'show cross sections through two furnaces with-several heating coils.Figures 5 and 6 are respectivelya longitudinal section 5 and a crosssection through a modified construction according to the invention.Figures 7 and 8 show in longitudinal section two different methods ofcooling for the new arrangement. Figure 9 shows another construction inperspective view. Figure 10 5 shows in longitudinal section anotherconstruction of the new arrangement. Figure 11 is a longitudinal sectionthrough a furnace with an inner and an outer heating coil. Figures 12and 13 are longitudinal sections through two other constructionsaccording to the invention.

In Figures 1 and 2, 1 is the metallic furnace jacket or casing, 2 therefractory linin of the furnace, 3 the inner hearth which is closed by acover 4. In the hearth 3 is arranged the high frequency coil 6 embeddedin a refractory hollow cylinder 5, so that it dips or is immersed intothe charge material 9. At 7 are indicated the insulated lead throughtubes of the coil 6. A pipe connection 8 makes it possible to produce avacuum or pressure in the interior of the furnace. The hollow cylinder 5containing the coil 6, 1's secured in any desired manner to the cover 4,the lower end of the hollow cylinder not touching the bottom of thehearth.

Themelting process in the furnace takes place in the following mannerThe eddy currents generated in the charge 1 material 9 by the coil 6carrying the high frequency currents and eventually also the hysteresis,heat the material contained in the interior of the refractory coil body5, as well as the material surrounding the refractory so coil body. Asthe density of the lines of force or flux in the interior of the coilbody is greater than in the molten material or charge surrounding thesame, the material in the coil body 5 will accordingly have highertemperatures than the material which surrounds the coil body 5. Afurther advantage of this method of heating is therefore that the mixingof the charge which becomes melted, takes place in an automatic 9%manner owing to the thermic equalization of the material havingdifferent specific gravities, which mixing assists the dynamic stirringaction which is produced as the consequence of the eddy currents in themolten charge. Figure 3 shows diagrammaticaly a modified construction ofthe new induction furnace. In this construction are provided threeheating coils 10, 11 and 12 embedded in refractory material, which inthe case of single phase current, must be connected together in series,and in the case of polyphase current, for instance three phase current,are situated each in one phase. This arrangement makes possible anintensive heating through of the bath at different points. Any desirednumber of such coils can be used, arranged as may be considered best ineach case and with regard to the metallurgical process to be carried outor to the heating process.

Figure 4 shows a furnace with two concentric induction coils 13 and 14enclosed in refractory material. In place of these two coils 13 and 14,there could also be used any desired number of such concentric coils,according to the strength of the heating efiect to be produced oraccording to the degree of duration of melting, the heating of thecoils, which is considered the most suitable, being effected by means ofa single phase or of a polyphase current. This arrangement has specialadvantages for large units, namely that for instance when the hearth islarge, the material contained in the same is uniformly heated in all thelayers, as in this construction there takes place a mutual action of themagnetic flux of the coils inwards and outwards.

In the same way such a heating device can be used with advantage forinstance for the purpose of heating various objects such as wire,cylinders, etc., a considerable saving in heating space'being at thesame time eflt'ected.

Figures 5 and 6 show the use of a flat coil or of any desired number offlat coils 15 which can be arranged at any desired depth of bath. Ifdesired, the level of the coils in the bath can be made adjustable, sothat, according to requirements, the single layers of the bath could beheated through. The coils 15 could be arranged above and next to eachother, and in the same way, the heating coils couldbe connected to asingle phase or to a polyphase current.

Figure 7 shows the arrangement of the coil 16 in the free space in theinterior of a hollow 1 body 17 of refractory material which can be (illsecured in a suitable manner to'the covering device 18 of the meltingchamber 19. The coil ends 20 and 21 project through thecovering device,and the pipe branches 22 and 23 enable gaseous medium to be injected forcooling the coil which can be made of any desirable shape in crosssection. Liquid coolin media can also be used.

igure 8 shows an arrangement of the coil similar to that of Figure 7with the difference however that the high frequency coil in Figure 8 isconstituted by a hollow conductor material of any desired cross section.The coil ends 25 and 26 project through the covering 27 of the heatingchamber 28. The cooling of the coil could be effected bythe use ofsuitable liquids or gases. In the constructions shown in Figures 7 and8, several coils can also be used in the heating chambers, and they canalso be connected to a single phase or to a polyphase current.

In the arrangements of the high frequency coils shown in Figures 7 and8, though only the magnetic flux of the outer coil field isutilized, theadvantage of all the other constructions is retained, namely thepossibility of using iron jacketing or reinforcements in. theconstruction of large furnace units, and moreover also the advantage ofuse of any desired number of heating coils.

Figure 9 shows the utilization of high frequency coils 29 in verticalarrangement in the heating chamber 30-, owing to which again can beensured a very uniform and energetic heating-through of the fusions bathor of the heating chamber and the coil can be connected to a singlephase or to a polyphase'alternating current.

In many cases it is'advisable to introduce the induction coil throughthe bottom of the furnace, .for instance into a hollow cylindricalinward projection at the bottom of the furnace, easily accessible fromthe outside, in such a manner that both the inner and the outer magneticfield of the coil passes arch a is arranged a cylindrical inwardprojection b accessible from the outside, into which is introduced theinduction coil 0. In this case, the coil 0 could be made of ordinarysolid wire or of hollow wire. It is arranged in such a manner that bothits inner and its outer magnetic field traverses the charge material (1.

1 In this arrangement, the induction coil can be cooled ina simplemanner by air or liquid, without any tight joints being required.Moreover, this arrangement has the advantage that it is completelyunnecessary to make in the furnace arch any openings such as requiredwhen introducing the coil from the top. Moreover, this constructionresults in a favourable distribution'of space, which is of particularimportance in the case of large furnaces. Finally the easy accessi- Whenused as a melting furnace, this arrangement offers the further advantagethat the molten mass is heated to the greatest ex,- tent in its bottomportion, so that circulation fromfthe top downward and back a inupwards, is automatically produced in t e molten mass, owing to which afavourable mixing is ensured.

The hollow cylindrical inward projection I) could also be 'detachablyinserted into the furnace bottom so that it could be replaced togetherwith the coil 0-, the coil 0 being embedded in it if desired. The coilcinstead of being made of solid wire of any desired shape, could also bemade of a hollow matescribed with reference to Fi ures 1 to 9.

It is further possible to eed one of the rial. 1

In addition toa heating coil immersed into the charge material, therecould be provided if desired a further coil which is placed round theoutsidewall ofthe furnace. This makes it possible considerably toincrease the heating effect, owing to the portion of the charge materialwhich is situated between the inner coil and the furnace wall, beingtraversed both by the inner magnetic flux of the coil at the outsidewall of the furnace, and by the outer magnetic field of the coilarranged in the interior of the hearth.

A construction of that kind is shown in Figure 11.

Round the outside wall 32 of the furnace, which is made of a refractorymaterial, is placed a coil 31 with the'connections 39. Inside thehearth33, which is closed by a cover 34, is mounteda second coil 36which is embedded in a hollow cylinder 35 of refractor material. In theconstruction illustrate the hollow cylinder 35 is secured to the cover34. Instead of that it could also be secured in a suitable manner to thebottom or to the walls of the furnace body. If desired, moreparticularly in the case of heating furnaces, the coil 36 could also bemounted on parts of the furnace without securing it. At 37 are indicatedthe insulated cover lead-through tubes of the coil 36. .A pipeconnection 38 makes it possible to produce a vacuum or a pressure in theinterior of the furnace.

The two coils 31 and 36 could be fed from the same or from differentsources of high frequency, for instance generators,.oscillationcircuits, etc. The feed currents for the coils 31 and-'36 could be ofthe sameor of different amplitude, and if desired also of differentfrequency, in order to obtain the best possible heating efiect. Thiseanbe done, when using a single high frequency generator, in a manner wellknown in itself by a different kind of coupling of the two circuitscontaining the coils 31 and 36, to thegenerator, or by using suitabledamping resistances etc. The outer coil 31 need enclose if desired onlya portion of the hearth or of a trough or the like connected to thesame.

This construction .makes it possible to increase or to reduce theHeating efiect as required, in a simple manner by switching in eitherboth coils or only one of the coils.

When using as melting furnace, first for instance the two coils 31 and36 can be switched in until the charge material has been melted.Thereupon, for instance the outer coil 31 can be switched off, in as faras the heating effect of the inner coil 36 is sufficient for the furtherheating of the molten metal. It is obvious that 1n the arrangementaccording to thisfigure, no closed iron casing can be used for thefurnace. For the rest however, any construction of the inner heatingcoil or heating coils can betused, which have been decoils 31 and 36with low frequency current, and the other with high frequency current,or also to feed both coils with low frequency current. For working underatmospheric pressure,'the furnace of this construction as well as of theconstruction according to Figure 1, can be built open, that is to saywithout cover.

The induction coil could also be covered inside and outside withrefractory material acting as support, in such a manner that it willallow of an easy expansion of the coil spires, more particularly in thedirection of the coil axis. This has the advantage that the ceramicmaterial enclosing the coil is not subjected to any stresses b the coil,as the single coil spires on being eated can freely expand. Asrefractory material there could be used zircon, carborundum, corundum,hi hlyrburnt fireclay or the like.

In igures 12 and 13 are shown two such constructions according to theinvention. In Figure 12, the heating coil 41 is arranged in the space 42between two hollow cylinders 43 and 44 of refractory material. The space42 is closed at the top and at the bottom by flange like projections 45and 46 of the hollow cylinders 43 and 44. At the places of contact, theparts 43, 45 and 44, 46 are caused to form tight joints with each other,for instance by cementin so that they form one unit containing t e coil41. The coil support thus formed is placed, in the constructionillustrated, on the bottom of the furnace 49. The bottom part of thecoil support is shown in elevation in order to make visible the openings50 which are required for a circulation of the molten metal from thespa;e iu the interior of the coil support, outwards. If desired, thecoil support could also be suspended in the furnace. This could be donefor instance by extending outwards the flange 45 of In place of that,the suspension of the coil support could be effected also by connectingit in a suitable manner to a furnace cover, so

; that it could be removed with the latter. In the constructionillustrated, the coil 41 is shown of tubular shape in order tofacilitate the cooling. The connections for the cooling device areindicated at 47 and 48 If desired an outer cooling of the coil 41 couldalso be effected, for instance by blowing air into thespace 42. Ifrequired, the walls of the coil 41 could be cooled fromthe outside aswell as from the inside.

Figure 13 shows another construction according to the invention. Atubular heating coil 51 is arranged in the space 52 between two hollowcylinders 53 and 54 of refractory material, which overlap each otherflange like at one end, at 55, and are closed at the other end by meansof a cover 561. The above mentioned parts are connected together to forma single unit and introduced into the interior of the furnace through arecessin the bottom of the furnace body 59, so that the cover 56 forms apart of the furnace bottom. At 57 and 58 are indicated theleading-through tubes which are used for connecting the coil 51, thecooling of which can be effected in the same way as indicated for thecoil 41, Figure 12. The coil support is secured in asuitable manner tothe furnace bottom and forms a tight joint with it. In order to ensure agood circulation of the liquid molten metal from the space in the in-.

terior of the hollow cylinder 53, outwards, in

- the hollow cylinders 53 and 54 are provided v material of tubularcross section of any shape,

the cooling being either by gas or by liquid. When air cooling is used,it is preferable to see that the surface of the coils is made as largeaspossible. vThe invention is chiefly intended for high frequencymelting furnaces or heating furnaces. It can be however appl1ed also forlow frequency working. The coils can be secured; either to the cover orto the lateral walls, or mounted in a suit able manner on the bottom, inwhich caseit is preferable always to leave a free space on all sidesbetween the coil body, on the one hand,

and the hearth bottom, cover, la.teral walls), on the other hand. Thecoil axes, instead of being vertical or horizontal,-could also be in-,cl nedat some other angle. For the generation. of the primary heatingcurrent there could be used dam ed or undamped vibrations. Theconnection of the coils could be effected either directly or throughtransformers or converters, to single phase or polyphase current. In thehearth, there could be used a pressure smaller or greater than or equalto the atmospheric.

What we claim as our invention and desire to secure by Letters Patentis:

1. A high frequency induction furnace or heating apparatus for thetreatment of metals or metal compounds, including an 1nduction coilarranged in the interior of the furnace and fed with high frequencycurrents, and a separating element consisting exclusively ofnon-metallic material between the outer surface of said coil andtheinterior of the furnace.

2. A high frequency induction furnace or heating apparatus for thetreatment of metals or metal compounds, including an in duction coilarranged in the interior of the furnace and fed with high frequencycurrents, a separating element consisting exclusively of non-metallicmaterial between the outer surface of said coil and the interior of thefurnace, and an additional separating element composed exclusively ofnon-metallic material between the inner surface of said coil and theinterior of the furnace.

3. A high frequency induction furnace or heating apparatus for thetreatment of metals or metal compounds, including acylindrical inductioncoil arranged in the interior of the furnace and fed with high frequencycurrents, and a hollow cylindrical body composed exclusively ofnon-metallic material and adapted to isolate both the inner and outersurfaces of said coil from the interior of the furnace.

4. A high frequency induction furnace or heating apparatus for thetreatment of metals or metal compounds, including a body of insulatingmaterial which projects into the interior of the furnace and a highfrequency induction coil supported by said body in such manner that saidcoil lies completely within the interior of the furnace.

5. A high frequency electric furnace comprising an insulated chamber, aninduction coil located inside said chamber, said coil bemg of the airwound type, and a furnace chamber external to said insulated chamber,

said coil and chamber being so designed that material placed in thefurnace chamber will be heated when current of high-frequency is appliedto the coil.

6. An induction furnace comprising a container for the charge, and atubular highfrequency coil extending into said container,

from above and terminating at a point above the bottom of the container,so that the charge may form a cont-inuous body located partly withinsaid coil and partly around the same, and so that both the inner and theouter ma etic fields of the coil will pass throu h t e charge.

7. n induction furnace comprising a container for the charge, a tubularcarrier of insulating material, open at the bottom,'extending into saidcontainer from above and terminating at a point above the bottom of thecontainer, so that the charge may form a 'tures.

VICTOR ENGELHARDT. REINHOLD GROSS.

y within said

